1. Field of the Invention
The present invention generally relates to blowing agent modifiers and their use. More specifically, the present invention is directed to blowing inhibitors and accelerators used to control chemical embossing of various coverings.
2. Description of Related Art
Chemical embossing has been used to create textured surface coverings for over 35 years and is well known in the art. The process of chemical embossing is described in U.S. Pat. No. 3,293,094 issued Dec. 20, 1966 (the xe2x80x9cNairn patentxe2x80x9d) and is herein incorporated by reference in its entirety. The Nairn patent discloses a process wherein a resinous composition (also referred to as a foamable polymer) containing a blowing agent mixed with a catalyst is deposited on a backing layer. The resinous layer is gelled at a temperature below the decomposition temperature of the blowing agent. An ink layer is deposited onto the gelled resinous layer by conventional printing or transfer methods. The resinous layer and ink layer form a chemical embossing layer. An optional wear layer may be deposited over the ink layer.
The ink layer includes regions containing a modifier that partially covers the resinous layer in a repeating or random pattern according to the desired design. The modifier diffuses into the gelled resinous layer directly below the modifier. The layers are then heat treated at a temperature sufficient to fuse the resinous layer and to decompose the blowing agent in the regions permeated by the modifier. The decomposition of the blowing agent creates gas pockets or bubbles in the foamable polymer that increase the thickness of the resinous layer in the permeated regions. The regions unaffected by the modifier do not expand as much as the permeated regions resulting in a textured surface containing expanded and substantially unexpanded regions in a pattern corresponding to the modifier pattern in the ink layer.
FIG. 1 is a cross-sectional schematic diagram of a surface covering described by Nairn prior to decomposition of the blowing agent. The surface covering 100 comprises a base layer 120 sandwiched between a backing layer 110 and an ink layer 130. An optional wear layer 140 covers the ink layer 130 and provides for increased wear and stain resistance for the surface covering 100. The base layer 120 comprises a resinous composition and a blowing agent. The ink layer 130 includes regions 135 containing a modifier that diffuses into the base layer 120 creating permeated regions 125 in the base layer 120.
FIG. 2 is a cross-sectional schematic diagram of a surface covering 200 described by Nairn after decomposition of the blowing agent has produced expanded regions 222 in the surface covering. The expanded regions 222 correspond to the permeated regions 125 of the un-expanded surface covering and are in register with the portions 135 of the ink layer 130 containing the modifier. As a result, the expanded surface covering 200 has a textured surface 250 arising from the variation in the base layer thickness between expanded regions 222 and un-expanded regions 224 of the base layer 220.
The selection of components comprising the embossing composition containing the modifier depends inter alia on the compositions of the blowing agent and the base layer resin composition. The Nairn patent discloses a simple test wherein candidate embossing compositions are deposited on a gelled base layer followed by heat treatment sufficient to fuse the base layer and decompose the blowing agent.
One blowing agent described by Nairn is azodicarbonamide. Azodicarbonamide decomposes between about 195-205xc2x0 C. The decomposition temperature may be lowered by adding a catalyst to the blowing agent. An example of a catalyst is ZnO.
Improved embossing compositions are disclosed in U.S. Pat. Nos. 5,336,693 issued Aug. 9, 1994, 5,531,944 issued Jul. 2, 1996, and 5,712,018 issued Jan. 27, 1998 (collectively referred to as the xe2x80x9cFrisch patentsxe2x80x9d) and are herein incorporated by reference in their entirety. The Frisch patents disclose an embossing composition comprising an aqueous suspension wherein the modifier is uniformly dispersed in the suspension as a substantially insoluble particulate solid.
U.S. Pat. Nos. 5,728,332 issued Mar. 17, 1998 and 5,733,630 issued Mar. 31, 1998 (collectively referred to as the xe2x80x9cFrisch et al. patentsxe2x80x9d) disclose an embossing composition incorporating modifiers that suppress the decomposition of the blowing agent and modifiers that accelerate the decomposition of the blowing agent and are herein incorporated by reference in their entirety.
The interaction between the blowing agent and modifier is sufficiently complex that empirical tests such as the test described by Nairn must be used to screen and confirm the effectiveness of the ink compositions. Such tests, however, cannot provide information relating to the mechanism by which the modifier affects the decomposition of the blowing agent nor whether the modifier acts directly on the blowing agent or on the accelerator. Although there are numerous compositions developed through empirical testing that are adequate for the manufacture of textured surface coatings, there still exists a need for compositions that allow for more accurate and precise control of the texturing process.
Accordingly, it is an object of the present invention to provide a new class of modifiers capable of inhibiting the activity of the catalyst and to provide a method for discovering such modifiers with determinable modifying characteristics.
One embodiment of the present invention is directed to a modifier for controlling decomposition of a blowing agent, the blowing agent characterized by a decomposition temperature, the modifier comprising a catalyst having an effective capability to reduce the blowing agent decomposition temperature and an organo-silane adsorbed onto the catalyst, the organo-silane capable of inhibiting the effectiveness of the catalyst.
Another embodiment of the present invention is directed to a gel layer for forming a chemical embossing layer of a multi-layer covering comprising: at least one foamable polymer; a blowing agent characterized by a decomposition temperature, the blowing agent capable of evolving gas and forming a plurality of bubbles in the foamable polymer during decomposition thereof; a catalyst capable of reducing the decomposition temperature of the blowing agent; and an organo-silane capable of modifying the capability of the catalyst to reduce the decomposition temperature of the blowing agent.
Another embodiment of the present invention is directed to a method for controlling decomposition of a blowing agent catalyzed by a catalyst, the blowing agent and catalyst mixed in a foamable polymer of a chemical embossing layer, the method comprising the steps of modifying the catalyst with an organo-silane and heating the chemical embossing layer, whereby the organo-silane regulates the decomposition of the blowing agent by the catalyst.
Another embodiment of the present invention is directed to a method of identifying a modifier for controlling activity of a catalyst for decomposition of a blowing agent, the method comprising the steps of: adsorbing a test compound onto the catalyst; measuring a decomposition temperature of the blowing agent heated in contact with the catalyst; and identifying the test compound as a modifier based on the measured decomposition temperature.
These above objects as well as other objects and features of the present invention will appear from the following description in which the preferred embodiments are set forth in detail in conjunction with the accompanying drawings.